Virtual Colonoscopy (cont.)
What is virtual colonoscopy?
Virtual colonoscopy is a technique that uses a
computerized tomographic (CT)
scan (a type of three-dimensional x-ray) to construct virtual images of the
colon that are similar to the views of the colon obtained by direct observation
by optical colonoscopy.
In preparation for virtual colonoscopy, the day before the examination the
colon is emptied using laxatives in a manner similar to optical colonoscopy.
During the examination, a small tube is inserted into the anus to inject and
fill the colon with air. Unlike with optical colonoscopy, this tube is not
advanced into the colon. The CT scan then is performed, and the scans are
manipulated by computer software to form virtual images of the colon. When
properly performed, virtual colonoscopy can be as effective as optical
colonoscopy. It can even find polyps "hiding" behind folds that occasionally are
missed by optical colonoscopy. The scanning takes only 10 minutes, and usually
no conscious sedation is necessary.
In October, 2007, researchers from University of Wisconsin published in the
New England Journal of Medicine a study comparing traditional optical
colonoscopy to virtual colonoscopy. More than six thousand patients over age 50
were evenly divided to undergo either optical or virtual colonoscopy. The
researchers found that virtual colonoscopy was as effective as optical
colonoscopy in detecting polyps larger than 5mm.
Comparing virtual colonoscopy and optical colonoscopy
- Virtual colonoscopy is less invasive and faster to perform than optical
colonoscopy and does not require conscious sedation.
- Even though virtual colonoscopy is less invasive than optical colonoscopy,
virtual colonoscopy still involves injecting air into the colon, which can be
uncomfortable for some patients. On the other hand, with adequate conscious
sedation, patients usually experience little or no discomfort with optical
colonoscopy.
- Virtual colonoscopy is not as reliable as optical colonoscopy in detecting
small polyps (less than 5mm in size). Even though most experts believe that
polyps smaller than 5mm are usually benign, some small polyps can be cancerous
or become cancerous if not removed.
- Virtual colonoscopy is not as accurate as colonoscopy in finding flat
cancers or polyps that are not protruding, that is, are not polyp-like.
- Virtual colonoscopy cannot remove polyps. If polyps are found by virtual
colonoscopy, then optical colonoscopy must be performed to remove the polyps.
Therefore, many individuals having virtual colonoscopy will have to undergo a
second procedure, optical colonoscopy.
- Even though the amount of radiation exposure with virtual colonoscopy is
considered safe, the long term radiation effects of mass screening with CT is
not known.
Next: My personal approach to recommending virtual versus optical
colonoscopies »
- Colonoscopy - Learn about the colonscopy procedure, what it is, why it is performed, preparation, complications, alternatives and the after effects of the screening exam on MedicineNet.com
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